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MCAT Biology Question — Neuron Functions

All of the following are true regarding the function of neurons EXCEPT:


A. Hyperpolarization at the end of an action potential is one mechanism by which neurons limit the rate at which action potentials may fire.
B. The flow of sodium into the neuron depolarizes the membrane in the first phase of an action potential.
C. The transmitting neuron secretes neurotransmitters, such as serotonin or dopamine, into the synaptic cleft from its dendrites.
D. An action potential is initiated when the axon hillock reaches the threshold potential.


Click for Explanation

This question is testing your understanding of the function of action potentials and neuronal transmission of signals. Here, (A), (B), and (D) are all true. Since this is an “EXCEPT” question, the right answer is the one false statement: choice (C). A neuron generally secretes neurotransmitters, like serotonin or dopamine, from its axon (specifically, from its axon terminal, or synaptic bouton). Retrograde neurotranmission (the secretion of neurotransmitters from dendrites) is rare, occurring mostly with nitric oxide and cannabinoid neurotransmitters.

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